I URGENTLY need advice!! life-changing experience!?

I need advice on a life-turning decision I must make now or never.

I am a 20 year old med school student currently living in Nicaragua and I have been in agreement with my routine-like lifestyle for 3 years, but I have never gotten the chance of doing something fun for myself. Therefore, I am planning to travel abroad by myself for my December break to Belize, and I have everything ready.

But there is a catch though, I don't know how to tell my parents! I am an only child and they seem to think that I don't know how to confront life by myself even though I am about to turn 21and I have gone through rough and tough! I mean, people would think that I am old enough to simply walk out the door whenever I want to without a word of explanation to my parents, but there are cultural reasons that stop me from doing this, and I don't know how to handle that!!

My inquiry is: should I try and tell my parents that I need to travel alone to experience life from a different perspective or should I just rebel out?? I am really wanting this experience more than anything and I need some advice. Thanks in advance :)